The objectives of this program are two-fold. First, we want to identify and obtain a preliminary characterization of new structural and regulatory alleles of the elements of the (Gus) complex. Second, we are surveying wild populations and ramdombred laboratory stocks for new haplotypes of the (Gus) complex and new allelic combinations within the complex. Once new haplotypes have been identified we are establishing these on congenic strain backgrounds for more complete characterizations. Four new (Gus) haplotypes have been discovered in our surveys of wild trapped mice. These have included three structural alleles not previously observed in wild mice, a new allele of the kidney androgen induction element Gus-rh and new alleles that identify a systemic regulatory element. Congenic strains carrying these (Gus) haplotypes have been constructed and are being used to identify the biochemical and kinetic properties of the induction and regulatory differences found in these mice. Continuing surveys of new sources of wild mice indicate that additional structural and regulatory combinations exist in the mouse gene pool that have not been characterized. Genetic characterizations and biochemical analyses of these resources are planned for the coming year.